The string that you can’t understand contains the unprintable
characters.
It is probably that you got if from some type of serialization.
You can say that is in a binary format but it’s not so good definition
because everything is in binary format - some we can read and some we
can not.

For the second question there is lot of strategies how to store the
array in a file and it most depend what do you want to do latter with
that stored information.
Nowadays is custom to use xml serialization, but you can use YAML or
JSON. They are all human readable.